This research focuses on the central unsolved problem of psychiatric epidemiology, the problem of how to measure psychiatric disorders independently of treatment status in general populations. Its goal is to develop adequate measurement procedures for the study of different types of symptomatology and related ability and disability in role functioning over time and in the context of changing social situations in contrasting social class and ethnic groups. The word "adequate" above is defined in terms of evidence of validity. Two main studies are involved: one completed; the other still in progress. The over 500 adult subjects from the completed study were drawn from five different ethnic groups, including Blacks and Puerto Ricans in the Washington Heights section of New York City. About 190 were psychiatric patients; 257 were members of community samples; and 67 were community leaders. These subjects were randomly alternated between two contrasting interview instruments, thereby permitting controlled comparisons of the results obtained by each. The interviews were conducted by 15 psychiatrists. The on-going study, based on the one described above, has involved construction of a composite interview instrument, test of it over time, and examination of the extent to which it can be administered by lay interviewers who are not clinicians rather than by psychiatrists. The subjects are a probability sample consisting of about 200 adults drawn from contrasting ethnic groups in the general population of New York City; the time period is one year. In addition, a parallel set of interviews have been conducted with an equivalent sample consisting of 126 adults who have provided "life change" ratings for stressful life events asked about in the above interviews, and also "social desirability ratings" for the items on symptomatology and role functioning.